Neural organization and neural interactions in mammalian retinas are investigated using intracellular electrophysiology, electron microscopy, and pharmacology. GABAergic effects have been investigated on horizontal, amacrine, and ganglion cells of cat retina. In all these cells GABA-A antagonists increase the speeds and amplitudes of transient responses while GABA-A agonists slow such responses. Actions on horizontal cells appear mediated by a receptor insensitive to bicuculline methyl halides. The influence of selective enhances rod signal components at low stimulus intensities while leaving unaffected cone signal components seen at high intensities. The D1 agonist SKF38393 also enhances rod signals at low concentrations, but at higher concentrations, suppresses cone signals in addition. These effects point to multifaceted regulation of outer-plexiform layer circuitry by both GABA and dopamine receptors. Biophysical properties of cat ON-beta ganglion cells were investigated by extrinsic current injection. Two response components were resolved: a short latency excitatory component and a longer latency, wider field inhibitory component. These combine to produce the signature transient- sustained depolarization seen with wide-field stimuli. Type b1 bipolars may provide excitation, while other bipolar or amacrine cells provide inhibition.